/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.planner.functions.aggfunctions;

import org.apache.flink.table.api.DataTypes;
import org.apache.flink.table.expressions.CallExpression;
import org.apache.flink.table.expressions.Expression;
import org.apache.flink.table.expressions.UnresolvedReferenceExpression;
import org.apache.flink.table.types.DataType;
import org.apache.flink.table.types.logical.DecimalType;
import org.apache.flink.table.types.logical.LocalZonedTimestampType;
import org.apache.flink.table.types.logical.TimeType;
import org.apache.flink.table.types.logical.TimestampType;

import java.util.Arrays;

import static org.apache.flink.table.expressions.ApiExpressionUtils.unresolvedRef;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.equalTo;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.greaterThan;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.ifThenElse;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.literal;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.minus;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.nullOf;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.or;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.plus;
import static org.apache.flink.table.planner.expressions.ExpressionBuilder.typeLiteral;
import static org.apache.flink.table.planner.functions.InternalFunctionDefinitions.THROW_EXCEPTION;

/** Base class for built-in single value aggregate function. */
public abstract class SingleValueAggFunction extends DeclarativeAggregateFunction {

    private static final long serialVersionUID = 8850662568341069949L;
    private static final Expression ZERO = literal(0, DataTypes.INT().notNull());
    private static final Expression ONE = literal(1, DataTypes.INT().notNull());
    private static final String ERROR_MSG =
            "SingleValueAggFunction received more than one element.";
    private UnresolvedReferenceExpression value = unresolvedRef("value");
    private UnresolvedReferenceExpression count = unresolvedRef("count");

    @Override
    public int operandCount() {
        return 1;
    }

    @Override
    public UnresolvedReferenceExpression[] aggBufferAttributes() {
        return new UnresolvedReferenceExpression[] {value, count};
    }

    @Override
    public DataType[] getAggBufferTypes() {
        return new DataType[] {getResultType(), DataTypes.INT()};
    }

    @Override
    public Expression[] initialValuesExpressions() {
        return new Expression[] {
            /* value = */ nullOf(getResultType()), /* count = */ ZERO,
        };
    }

    @Override
    public Expression[] accumulateExpressions() {
        return new Expression[] {
            /* value = count > 0 ? exception : operand(0) */
            ifThenElse(
                    greaterThan(count, ZERO),
                    throwException(ERROR_MSG, getResultType()),
                    operand(0)),
            /* count = count + 1 */
            plus(count, ONE)
        };
    }

    @Override
    public Expression[] retractExpressions() {
        return new Expression[] {
            /* value = count == 1 || count == 0 ? null : exception */
            ifThenElse(
                    or(equalTo(count, ONE), equalTo(count, ZERO)),
                    nullOf(getResultType()),
                    throwException(ERROR_MSG, getResultType())),
            /* count = count - 1 */
            minus(count, ONE)
        };
    }

    @Override
    public Expression[] mergeExpressions() {
        return new Expression[] {
            ifThenElse(
                    greaterThan(plus(count, mergeOperand(count)), ONE),
                    throwException(ERROR_MSG, getResultType()),
                    ifThenElse(
                            equalTo(plus(count, mergeOperand(count)), ZERO),
                            ifThenElse(
                                    // both zero or right > 0 means we need to reserve the new value
                                    // here
                                    or(
                                            equalTo(count, ZERO),
                                            greaterThan(mergeOperand(count), ZERO)),
                                    mergeOperand(value),
                                    nullOf(getResultType())),
                            mergeOperand(value))),
            plus(count, mergeOperand(count))
        };
    }

    @Override
    public Expression getValueExpression() {
        return value;
    }

    private static Expression throwException(String msg, DataType type) {
        // it is the internal function without catalog.
        // so it can not be find in any catalog or built-in functions.
        return new CallExpression(
                THROW_EXCEPTION, Arrays.asList(literal(msg), typeLiteral(type)), type);
    }

    /** Built-in byte single value aggregate function. */
    public static final class ByteSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.TINYINT();
        }
    }

    /** Built-in short single value aggregate function. */
    public static final class ShortSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.SMALLINT();
        }
    }

    /** Built-in int single value aggregate function. */
    public static final class IntSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.INT();
        }
    }

    /** Built-in long single value aggregate function. */
    public static final class LongSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.BIGINT();
        }
    }

    /** Built-in float single value aggregate function. */
    public static final class FloatSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.FLOAT();
        }
    }

    /** Built-in double single value aggregate function. */
    public static final class DoubleSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.DOUBLE();
        }
    }

    /** Built-in boolean single value aggregate function. */
    public static final class BooleanSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.BOOLEAN();
        }
    }

    /** Built-in decimal single value aggregate function. */
    public static final class DecimalSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        private final DecimalType type;

        public DecimalSingleValueAggFunction(DecimalType type) {
            this.type = type;
        }

        @Override
        public DataType getResultType() {
            return DataTypes.DECIMAL(type.getPrecision(), type.getScale());
        }
    }

    /** Built-in string single value aggregate function. */
    public static final class StringSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.STRING();
        }
    }

    /** Built-in date single value aggregate function. */
    public static final class DateSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.DATE();
        }
    }

    /** Built-in time single value aggregate function. */
    public static final class TimeSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        @Override
        public DataType getResultType() {
            return DataTypes.TIME(TimeType.DEFAULT_PRECISION);
        }
    }

    /** Built-in timestamp single value aggregate function. */
    public static final class TimestampSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 320495723666949978L;

        private final TimestampType type;

        public TimestampSingleValueAggFunction(TimestampType type) {
            this.type = type;
        }

        @Override
        public DataType getResultType() {
            return DataTypes.TIMESTAMP(type.getPrecision());
        }
    }

    /** Built-in timestampLtz single value aggregate function. */
    public static final class TimestampLtzSingleValueAggFunction extends SingleValueAggFunction {

        private static final long serialVersionUID = 1L;

        private final LocalZonedTimestampType type;

        public TimestampLtzSingleValueAggFunction(LocalZonedTimestampType type) {
            this.type = type;
        }

        @Override
        public DataType getResultType() {
            return DataTypes.TIMESTAMP_LTZ(type.getPrecision());
        }
    }
}
